Preheat oven to 350. Paper line 18 muffin cups. Combine flour, granulated sgar, brown sugar, baking powder and salt in large bowl. Stir in milk, egg, butter and lemon peel. Stir in 1 1/2 cups morsels and blueberries. Spoon into prepared muffin cups, filling almost full. Sprinkle with streusel topping. Streusel-you mix 1/3 cup granulated sugar, 1/4 cup all-purpose flour and 1/4 tsp ground cinnamon in small bowl. Cut in 3 Tbsp. butter with pastry blender and sprinkle crumbs on top.
Bake for 22 to 25 minutes or until center test done. Cool in pans for 5 minutes; remove to wire racks to cool slightly.
Place remaining morsels in small, heavy duty resealable plastic ziplock bag, microwave on medium high 70% power for 30 seconds; knead. Microwave at 10 to 15 second intervals, kneading until smooth. Cut tiny corner from bag; squeeze to drizzle over muffins. Seve warm.